Method for removing phospholipids from vegetable oil miscella, method for conditioning a polymeric microfiltration membrane, and membrane

ABSTRACT

A method for removing phospholipids from vegetable oil miscella is provided. The method includes steps of feeding vegetable oil miscella to a conditioned polymeric microfiltration membrane, and recovering a permeate stream having a decreased weight percent of phospholipids compared with the weight percent of phospholipids provided in the miscella. The polymeric microfiltration membrane can be conditioned for the selective separation of phospholipids in the miscella. A method for conditioning a membrane for selective separation of phospholipids from vegetable oil miscella, and the resulting membrane, are provided. The membrane which can be conditioned can be characterized as having an average pore size of between about 0.1μ and about 2μ.

FIELD OF THE INVENTION

[0001] The invention relates to a method for removing phospholipids fromvegetable oil miscella, a method for conditioning a polymericmicrofiltration membrane for selective removal of phospholipids frommiscella, and membrane.

BACKGROUND OF THE INVENTION

[0002] Edible vegetable oils are generally obtained by processing oilseeds. Crude vegetable oils can be obtained from vegetable seeds bysolvent extraction. Hexane is the most commonly used extraction solvent.The crude vegetable oils generally contain neutral triglycerides and ahost of natural contaminants including phosphotides, sulphurouscompounds, free fatty acids, carbohydrates, peptides, oxidized lipids,traces of lower aldehydes and ketones, glycosides of sterols andterpenes, and diverse types of color bodies or dyestuffs. Thesecontaminants are removed from the crude vegetable oils in the course ofrefining in order to render the vegetable oils palatable.

[0003] The recovery of soybean oil from soybeans is particularlydesirable. A technique for recovering soybean oil includes severalprocessing steps. The soybean is dehulled and crude soybean oil isextracted with hexane. The extractant (miscella), which includes hexaneand crude soybean oil, is further processing to recover palatablesoybean oil. The hexane is evaporated from the miscella and theresulting crude soybean oil is degummed. Degumming, as used inconventional processes, refers to the removal of phasphatides and othergums from the oil by adding water and/or acid thereto and centrifuging.The recovered oil can be further refined with water and alkaline (suchas NaOH) and centrifuged to remove the fatty acids and gums. The oilresulting from the alkaline refining step can then be bleached to removecolor bodies, hydrogenated to render the oils more stable, anddeodorized. The techniques of degumming, alkaline refining, bleaching,hydrogenating, and deodorizing are well known in the art. It should beappreciated that each separation step, and particularly centrifuging,results in loss of oil.

[0004] Numerous prior art references describe techniques for obtainingvegetable oils by application of membrane technology. For example, U.S.Pat. No. 4,093,540 to Sen Gupta describes refining crude glyceride oilsby contacting a composition of glyceride oils and organic solvent underpressure with a semi-permeable ultrafiltration membrane to separateconstituents of different molecular weight into retentate and permeatefractions, and contacting the composition or at least one of thefractions with a metal oxide or metalloid oxide adsorbent in a columncontaining the adsorbent. Additional references which describe the useof membrane technology for separating phospholipids from crude vegetableoils include: U.S. Pat. Nos. 4,414,157 to Iwama et al.; 4,533,501 to SenGupta; Raman et al., “Membrane Technology”, Oils & Fats International,Vol. 10, No. 6, 1994, pages. 28-40; Ziegelitz, “Lecithin ProcessingPossibilities”, Inform, Vol. 6, No. 11, November 1995, pages. 1224-1213;Ondrey et al., “The Skinny On Oils & Fats”, Chemical Engineering,October 1997, pages. 34-39; Pioch et al., “Towards An Efficient MembraneBased Vegetable Oils Refining”, Industrial Crops & Products, 7 (1998)pages 83-89; Koseoglu et al., “Membrane Applications & Research In TheEdible Oil Industry: And Assessment, JAOCS, Vol. 67, No. 4 (April 1990),pages 239-249.

SUMMARY OF THE INVENTION

[0005] A method for removing phospholipids from vegetable oil miscellais provided by the present invention. The method includes a step offeeding vegetable oil miscella to a membrane for recovery of a permeatestream and a retentate stream, and recovering the permeate stream havingdecreased weight percent of phospholipids compared with the weightpercent of phospholipids provided in the miscella.

[0006] In the context of the present invention, the permeate stream isthe stream which flows through the membrane, and the retentate stream isthe stream which does not flow through the membrane. The vegetable oilmiscella includes extraction solvent and crude vegetable oils containingphospholipids. The membrane includes a polymeric microfiltrationmembrane conditioned for selective separation of phospholipids from themiscella to provide a permeate stream having a decreased weight percentof phospholipids compared with the weight percent of phospholipidsprovided in the miscella. The microfiltration membrane, prior tomodification, is preferably provided having an average pore size in therange of about 0.1μ to about 2μ.

[0007] The vegetable oil miscella preferably contains between about 45percent by weight and about 90 percent by weight extraction solvent, andmore preferably between about 70 percent by weight and about 80 percentby weight extraction solvent. A preferred extraction solvent includeshexane. The permeate stream preferably includes less than 0.6 weightpercent phospholipids, more preferably less than about 0.15 weightpercent phospholipids, and even more preferably less than about 0.015weight percent phospholipids.

[0008] A method for conditioning a microfiltration membrane is providedby the invention. The method includes providing a polymericmicrofiltration membrane characterized as having an average pore size inthe range of about 0.1μ to about 2μ. Preferably, the polymericmicrofiltration membrane comprises polyacrylonitrile, polysulfone,polyamide, or polyimide. The polymeric microfiltration membrane can beconditioned by treating the membrane with an intermediate solvent, andthen treating the membrane with an extraction solvent. A preferredembodiment of the invention includes treating the membrane with amixture of intermediate solvent and extraction solvent between the stepsof treating the membrane with an intermediate solvent and treating themembrane with an extraction solvent.

[0009] The steps of treating the membrane with solvent are conducted fora period of time which is sufficient to provide the desired level ofconditioning. In most cases, it is expected that the treatment willinclude flushing and/or soaking for at least about one-half hour. Forconvenience, it may be desirable to allow the membrane to soak in theparticular solvent over night or for a period of up to about 24 hours.It should be understood that longer soaking times are permitted.

[0010] The treatment with the intermediate solvent is advantageous toreduce the likelihood of shocking or harming the membrane when treatedwith the extraction solvent. Exemplary intermediate solvents includealcohols and acetone. Preferably, the intermediate solvent is one whichis miscible with the extraction solvent. In the case of using hexane asthe extraction solvent, the intermediate solvent is preferably ethanol,propanol or a mixture of ethanol and propanol.

[0011] A conditioned polymeric microfiltration membrane is provided bythe invention. The conditioned membrane can be characterized as amembrane resulting from the steps of conditioning. In addition, theconditioned membrane can be characterized in terms of its performance.For example, a soybean oil miscella can be providing containing 25percent by weight crude soybean oil and 75 percent by weight hexane, andcontaining a phosphorous level of about 5,000 ppm in the crude oil. Byfeeding the miscella to the membrane at a transmembrane pressure ofabout 150 psi, it is expected that the membrane will provide a steadystate permeate at a flux of greater than about 65 l/hr m² and aphosphorous level of less than about 50 ppm. Preferably, the phosphorouslevel will be less than about 25 ppm. More preferably, the flux will begreater than about 80 l/hr m².

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a diagrammatic representation of a method for removingphospholipids from vegetable oil miscella according to the principles ofthe present invention; and

[0013]FIG. 2 is a diagrammatic representation of a prior art method forremoving phospholipids from vegetable oil miscella utilizing acid andalkaline treatment.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The invention relates to a method for degumming vegetable oilmiscella. Vegetable oil miscella can be referred to herein more simplyas miscella. Miscella refers to the extractant resulting from solventextraction of vegetable seeds. The miscella generally includesextraction solvent, crude vegetable oils obtained by extraction from thevegetable seeds, and meal fines resulting from the ground vegetableseeds. Techniques for solvent extraction of vegetable seeds are wellknown and are described, for example, in Bailey's Industrial Oil and FatProducts, 5th Edition, edited by Y. H. Hui, New York, Wiley, 1996, andHandbook of Soy Oil Processing and Utilization, St. Louis, Mo., AmericanSoybean Association, Champaign, Ill., American Oil Chemists' Society,the disclosures of which are incorporated herein by reference.

[0015] The preferred vegetable oils which can be isolated according tothe present invention are the edible vegetable oils which are well-knownin the vegetable oil industry. Exemplary vegetable oils include coconutoil, palm oil, palm kernel oil, soya bean oil, corn oil, ground nut oil,olive oil, linseed oil, rapeseed oil, sunflower seed oil, safflower seedoil, cottonseed oil, and grape seed oil. Preferred oils which can berecovered according to the invention include soya bean oil, rapeseedoil, ground nut oil, corn oil, sunflower oil, cottonseed oil, andlinseed oil.

[0016] In order to recover edible vegetable oils from the miscella, thephospholipids are removed. The technique for removing phospholipids frommiscella can be referred to as miscella degumming. While a feature ofthe invention relates to removal of phospholipids from miscella, itshould be appreciated that other impurities in the miscella canadditionally be removed by the invention. In particular, significantamounts of color bodies and free fatty acids provided in the miscellacan be removed by the technique of removing phospholipids from vegetableoil miscella according to the invention.

[0017] The solvent which can be used for extracting crude vegetable oilsfrom crushed vegetable seeds is one in which the vegetable oils readilysolubilize. Such solvents are well-known in the industry. The solvent ispreferably one having a comparatively low molecular weight. That is, amolecular weight which is not substantially more than that of thevegetable oil. Preferably, the molecular weight of the solvent isbetween about 50 and about 200, and more preferably between about 60 andabout 150. Solvents of low molecular weight, e.g., esters andhalohydrocarbons, can be used but preferred solvents include inerthydrocarbons, particularly alkanes, cycloalkenes, and simple aromatichydrocarbons, e.g., benzene and its homologues containing alkylsubstituents having up to four carbon atoms. These solvents tend toimprove the mobility of the oil and bringing about a transformation ofany phospholipid molecules present to form micelles. This phenomena,which can be described as aggregation of a large number of phospholipidmolecules under the influence of the solvent to bodies (micelles) ofhigh molecular weight which can be as high as 200,000 in hexane, greatlyincreases the effective particle size of the phospholipids, enablingthem to be wholly retained by membranes permitting the free passage ofthe oil and solvent present. Moreover, the micelles thus formed appearto imbed the comparatively small molecules of other impurities such assugars and amino acids which might otherwise escape with the oil throughthe membrane. Exemplary hydrocarbons include benzene, toluene, xylenes,cycloalkanes such as, cyclohexane, cyclopentane, and cyclopropane, andalkanes, such as pentanes, hexanes, butanes and octanes in mixturesthereof, petroleum ether boiling between the range of −1° C. and 120° C.or alkenes.

[0018] While it is preferred to use hydrocarbons which are normallyliquid at ambient temperatures, other solvents may be used which areliquid only under the filtration pressure used. Where the oil is to beseparated by evaporating off the solvent, the solvent is preferably ofcomparatively low boiling point. Where phosphotides are not present insignificant amounts, other organic solvents including acetone may beused.

[0019] The amount of solvent is the miscella is generally provided as aresult of extracting crude vegetable oils from vegetable seeds.Accordingly, the amount of solvent present in the miscella may varydepending upon the particular solvent extraction design utilized. Whilean amount of solvent can be removed from the miscella prior to degummingthe miscella, it is preferred that a sufficient amount of solvent remainwhich allows the miscella to flow through a separation membrane. Ingeneral, it is expected that the miscella will include an amount ofsolvent of between about 45 percent by weight and about 90 percent byweight, and more preferably between about 70 percent by weight and about80 percent by weight.

Removing Phospholipids

[0020] Now referring to FIG. 1, a method for removing phospholipids fromvegetable oil miscella according to the invention is provided atreference numeral 10. Oil seeds are prepared for extraction usingtechniques well known in the art. Oil seeds 11 are processed in apreparation unit 12. This generally includes dehulling and/or grinding.Crude vegetable oil 14 can be obtained from certain types of vegetableoils by expelling in an expeller unit 15. Accordingly, the ground oilseeds 13 can be fed to an expeller 15 to provide crude vegetable oil 14.It should be understood that crude vegetable oil is generally notobtained from all types of oil seeds by expelling. Accordingly, theground oil seeds 13′ can be sent directly to an extractor 18, bypassingthe expeller 15. In addition, expelled cake 16 can be processed for therecovery of crude vegetable oil by extraction.

[0021] A solvent 19 is introduced into the extractor 18 and miscella 20is recovered. The miscella 20 includes, as major constituents,extraction solvent, vegetable oils, and phospholipids. Techniques forforming miscella by solvent extraction of vegetable oil seeds aregenerally known in the art. If desired, the expelled crude oil 14 can becombined with the miscella 20 for further processing.

[0022] The phospholipids can be removed from the miscella 20 by feedingthe miscella 20 to a filter 22 which includes a separation membrane. Theseparation membrane is preferably a polymeric microfiltration membranewhich has been conditioned to selectively remove phospholipids from themiscella 20. Details of the separation membrane and techniques forproviding the conditioning for selective removal of phospholipids aredescribed below.

[0023] The separation membrane can be provided in any form which canprovide the desired degree of miscella degumming. In general, membranesare available as spiral wound membranes, tubular membranes, and flatplate membranes. For the removal of phospholipids from miscella, spiralwound membranes are preferred because they are generally more costeffective than other filter designs.

[0024] A permeate stream 24 flows from the filter 22 and includesvegetable oils and extraction solvent having a decreased concentrationof phospholipids. The retentate stream 26 flows from the filter 22 andincludes vegetable oils and extraction solvent and an increasedconcentration of phospholipids. The filtration system can be a batch orcontinuous. A preferred type of continuous filtration system includes afeed and bleed system.

[0025] The permeate stream 24 is fed to an evaporator 28 for removal ofthe extraction solvent. The resulting vegetable oil stream 30 can betreated by steps of refining, bleaching, hydrogenating, and deodorizingwhich are generally known in the art. Such techniques are described, forexample, in the Handbook of Soy Oil Processing and Utilization, St.Louis, Mo., American Soybean Association, Champaign, Ill, American OilChemists' Society.

[0026] The method of the invention can be used to provide a resultingvegetable oil stream 30 containing a desired level of phospholipids.Typically, commercially degummed vegetable oil has a phosphorous levelof less than 100 ppm. In general, lower levels of phosphorous invegetable oil are desirable. The method of the invention can provide avegetable oil stream 30 having a phosphorous level of less than 30 ppm,and more preferably less than 5 ppm.

[0027] Now referring to FIG. 2, a prior art method for removingphospholipids form vegetable oil miscella is shown at reference numeral50. This prior art process is shown to provide a comparison with theprocess of the invention. In general, oil seeds 51 are processed in apreparation unit 52, and, if desired, the ground seeds 53 are subject toexpelling in an expeller 54. The ground seeds 53′ and/or the expelledcake 55 is fed to an extractor 56, along with an extraction solvent 58,and miscella 60 is recovered. The solvent 58 is recovered from themiscella in an evaporator 62. The resulting crude oil 66 (which can alsobe obtained from the expeller 54 for certain types of oil seeds) issubjected to water 68 and acid 70 treatment in order to hydrate thephospholipids. The water and acid treated crude oil is processed in acentrifuge 71 to remove the hydrated gums 73. The resulting degummedstream 72 is generally treated with aqueous alkaline for neutralizationand further centrifuging. The resulting oil is then typically bleached,hydrogenated, and deodorized.

Membrane Conditioning

[0028] The invention relates to the conditioning of a polymericmicrofiltration membrane for the selective removal of phospholipids fromvegetable oil miscella. The conditioned polymeric microfiltrationmembrane can be referred to herein as the conditioned membrane.

[0029] Membranes generally act as filters for preventing the flowtherethrough of particular sized components. The membranes can becharacterized in terms of their average pore size. For example,membranes having an average pore size of between about 0.1μ and about 2μare referred to as microfilters or microfiltration membranes; membraneshaving an average pore size of between about 10,000 mwco (molecularweight cut-off using Dextran) and about 0.1μ are referred to asultrafilters or ultrafiltration membranes; membranes having an averagepore size of between about 200 mwco and about 10,000 mwco are referredto as nanofilters; and membranes that can remove components of below 200mwco are referred to as reverse osmosis membranes.

[0030] Applicants discovered that by conditioning a microfiltrationmembrane, the membrane can be provided for selectively removingphospholipids from miscella. Furthermore, the flux across the membraneis increased at a given transmembrane pressure compared with the use ofan ultrafiltration membrane for removal of phospholipids from miscella.Alternatively, the use of a conditioned microfiltration membrane canprovide a lower transmembrane pressure at a given flux across themembrane compared with the use of an ultrafiltration membrane.

[0031] The microfiltration membrane is preferably conditioned bysuccessive solvent treatments. In general, commercially availablepolymeric microfiltration membranes are delivered from the manufacturersoaking in water or glycerol. The successive treatment of the membraneis provided for conditioning the membrane so it will function in themiscella. That is, the membrane should be conditioned so that it willnot react adversely when contacted with the extraction solvent providedin the miscella. In cases where the membrane would be shocked byplacement directly in the extraction solvent for conditioning, anintermediate solvent can be used to provide a first level ofconditioning before the membrane is introduced into the extractionsolvent.

[0032] The treatment of the microfiltration membrane is provided forgradually changing the polarity of the membrane. Accordingly, thetreatment can involve flushing with a solvent, soaking in a solvent, ora combination thereof. Furthermore, the treatment can include successivetreatment with different solvents or blends of solvents to provide themodified membrane.

[0033] In a preferred method for conditioning a polymericmicrofiltration membrane, the membrane is preferably first soaked in anintermediate solvent, such as an alcohol. Preferred alcohols which canbe used as the intermediate solvent include ethanol, propanol,isopropanol, butanol, octanol, and mixtures thereof. Preferred alcoholsare those which are miscible with the extraction solvent. In the casewhere hexane is the extraction solvent, a preferred intermediate solventincludes ethanol, propanol, and a mixture of ethanol and propanol. Anon-alcohol intermediate solvent includes acetone.

[0034] Prior to the soaking, the membrane can be flushed withintermediate solvent to remove water or glycerol or other solvent inwhich the membrane is provided. The membrane is then preferably soakedin a mixture of intermediate solvent and extraction solvent. When hexaneis the extraction solvent, the mixture preferably includes about 50percent by weight ethanol and 50 percent by weight hexane. The membraneis then flushed with the extraction solvent to remove the intermediatesolvent. The membrane can then be used according to the invention. Itshould be appreciate that while a preferred embodiment of the inventionis described in the context providing at least three separate treatmentsteps, the invention can be practiced by treating the membrane in anintermediate solvent and then treating the membrane in the extractionsolvent. Furthermore, it should be understood that the extractionsolvent refers to the solvent provided in the miscella. Thus, theextraction solvent in the miscella can contribute to the treatment ofthe membrane.

[0035] It should be appreciated that the length of treatment of themembrane in a particular solvent should be sufficient to provide thedesired level of conditioning in that step. For example, it is expectedthat the step of treating the membrane in an intermediate solvent can beprovided in 10 minutes. It is convenient, however, to allow the membraneto soak for at least one-half hour, and more preferably about 5 hours toabout 24 hours. It is expected that the step of treating the membrane ina mixture of intermediate solvent and extraction solvent can be providedin 10 minutes, but is conveniently provided for up to about 5 hours or24 hours. Furthermore, it is expected that the step of treating themembrane in the extraction solvent is can be provided to removeintermediate solvent. It is expected that flushing the membrane withextraction solvent to remove intermediate solvent will take place inabout 10 minutes. However, it is convenient to allow the membrane tosoak in extraction solvent for about 5 hour or up to about 24 hours.

[0036] After the membrane has been used according to the invention, itcan be cleaned and regenerated by treating with extraction solvent. Ingeneral, it is expected that the membrane can be used for removingphospholipids from miscella in a continuous filtration operation for atleast about 24 hours before cleaning the membrane in the extractionsolvent for a period of time generally less than one-half hour. Themembrane can be cleaned by flushing with extraction solvent for anamount of time sufficient to remove phospholipids from the membrane. Itis expected that the membrane can be cleaned by flushing in extractionsolvent for about 10 minutes. Furthermore, the cleaning time in theextraction solvent can be provided for greater than one-half hours. Inaddition, it should be appreciated that rather than using pureextraction solvent to flush the membrane for cleaning, it is expectedthat fresh miscella which has not been concentrated can be used forcleaning the membrane. In general, miscella obtained directly from anextractor can be referred to as unconcentrated miscella. Furthermore, itis expected that an acid can be added to the extraction solvent orunconcentrated miscella in order to assist the cleaning. For example,citric acid, phosphoric acid, lactic acid, or sulfuric acid can be addedto extraction solvent in an amount of about 0.1 or about 0.2 percent byweight to provide assistance in cleaning.

[0037] Membranes which can be used according to the invention include a0.3μ polyacrylonitrile (PAN) membrane available from Osmonics, Inc. ofMinnetonka, Minn., and a 0.1μ polysulfone (PS) membrane which isavailable from Hoechst Separation Product of Wiesbaden, Germany. Otherpolymeric microfiltration membranes such as polyamide (PA) and polyimide(PI) can also be used according to the invention.

[0038] A preferred extraction solvent which can be used for conditioningthe membrane includes hexane. It should be appreciated that thereference to hexane includes the isomers of hexane such as isohexane andn-hexane. In addition, the extraction solvent can include isopropanol.

[0039] The conditioned membrane of the invention can be characterized interms of its performance. For example, a soybean oil miscella feedcharacterized by 25 percent by weight crude soybean oil and 75 percentby weight hexane, and having a phosphorus level of about 5,000 ppm(based on the crude oil) and provided at a transmembrane pressure of 150psi, can be filtered through the membrane to provide a permeate at aflux of greater than 65 l/hr m² and a phosphorous level of less thanabout 50 ppm. Preferably, the flux will be greater than 80 l/hr m². Morepreferably, the level of phosphorous in the permeate will be less thanabout 25 ppm. For a corn oil miscella containing 25 percent by weightcrude corn oil and 75 percent by weight hexane, and a phosphorous levelof about 13,200 ppm at 150 psi, a filtrate will be provided at a flux ofgreater than about 65 l/hr m² having a phosphorous level of less thanabout 50 ppm. Preferably, the flux will be greater than about 75 l/hrm². Furthermore, the level of phosphorous in the permeate is preferablyless than about 25 ppm. It should be appreciated that theabove-identified flux values are provided under steady state conditions.

[0040] The performance of the conditioned membrane of the invention issupported by the following example. It should be understood that theexample is not intended to limit the scope of the invention.

EXAMPLE

[0041] Three samples of miscella were prepared by using the presenttechniques. Miscella samples were obtained from three different oilseeds plants.

[0042] A membrane was conditioned and used for removing phospholipidsfrom each of the three samples of miscella. The membrane purchased was aPAN membrane from Osmonics, Inc. The membrane can be characterized ashaving an average pore size of 0.3μ, and in the form of a spiral wound25×40 membrane element. The membrane was conditioned by soaking themembrane in an intermediate solvent (propanol) for 24 hours. Then themembrane was soaked in mixture of intermediate solvent (propanol) andextraction solvent (hexane) for 24 hours. Finally, the membrane wassoaked in extraction solvent (hexane) for 24 hours.

[0043] The three samples of miscella were individually processed. Forthe soy bean oil miscella and the canola oil miscella, test wasconducted at retentate concentration of 10 X of the feed concentration.The permeate rate at 10 X concentration was 100 l/hr m² and 66 l/hr m²for soy bean miscella and canola oil miscella, respectively. For thecorn oil, the test was conducted at retentate concentration of 7.4 X ofthe feed at permeate rate of 80 l/hr m². The feed and permeate wereanalyzed, and the results are reported in table 1. TABLE 1 Analysis ofMiscella Membrane Degummed Oil Soybean Canola oil oil Corn oilExtracted + Extracted Extracted Prep Feed Permeate Feed Permeate FeedPermeate phosphorous 545 21 1783 41.2 505 24.4 ppm Ca, ppm 34.2 1.7 14.40.83 137.5 8.05 Mg, ppm 26 1.68 264.4 5.54 82.4 4.36 FFA, wt % 0.35 0.142.88 1.78 0.58 0.46 Chlorophyll, 391 ppb 126 ppb NA NA 16.1 10.1 ppm ppmRed 13 9.3 70* 30 — 4.0* Yellow 40 30 21.5 15.6 — 70* % Solvent in 75 7575 75 60 60 Miscella Filtration 100⁽¹⁾ 80⁽²⁾ 66⁽¹⁾ Rate L/hr. m²

[0044] The above specification, examples and data provide a completedescription of the manufacture and use of the composition of theinvention. Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended.

We claim:
 1. A method for removing phospholipids from vegetable oilmiscella, the method comprising steps of: (a) feeding vegetable oilmiscella to a membrane for recovery of a permeate stream and a retentatestream, wherein said miscella comprises extraction solvent and crudevegetable oil containing phospholipids, and said membrane comprises apolymeric microfiltration membrane conditioned for selective separationof phospholipids from said miscella to provide a permeate stream havingdecreased weight percent of phospholipids compared with the weightpercent of phospholipids provided in said miscella; (b) recovering saidpermeate stream having decreased weight percent of phospholipidscompared with the weight percent of phospholipids provided in saidmiscella.
 2. A method for removing phospholipids from vegetable oilmiscella according to claim 1 , wherein the microfiltration membranecomprises a membrane provided on a backing, the membrane characterizedas having an average pore size in the range of about 0.1μ to about 2μ.3. A method for removing phospholipids from vegetable oil miscellaaccording to claim 2 , wherein the polymeric microfiltration membrane isconditioned by a three step conditioning sequence comprising: (i)treating the microfilter with an intermediate solvent; and (ii) treatingthe microfilter with a mixture of intermediate solvent and extractionsolvent; and (iii) treating the microfilter with an extraction solvent.4. A method for removing phospholipids from vegetable oil miscellaaccording to claim 1 , wherein said miscella comprises between about 45and about 90 weight percent extraction solvent.
 5. A method for removingphospholipids from vegetable oil miscella according to claim 1 , whereinthe extraction solvent comprises hexane.
 6. A method for removingphospholipids from vegetable oil miscella according to claim 1 , whereinsaid permeate stream comprises less than about 0.6 weight percentphospholipids.
 7. A method for removing phospholipids from vegetable oilmiscella according to claim 1 , wherein said permeate stream comprisesless than about 0.15 weight percent phospholipids.
 8. A method forremoving phospholipids from vegetable oil miscella according to claim 1, wherein said permeate stream comprises less than 0.015 weight percentphospholipids.
 9. A method for removing phospholipids from vegetable oilmiscella according to claim 1 , wherein the microfiltration membranecomprises polyacrylonitrile, polysulfone, polyamide, or polyimide.
 10. Amethod for conditioning a polymeric microfiltration membrane forselective separation of phospholipids from vegetable oil miscella, themethod comprising steps of: (a) providing a polymeric microfiltrationmembrane characterized as having an average pore size in the range ofabout 0.1μ to about 2μ; (b) treating the membrane with an intermediatesolvent; and (c) treating the membrane with an extraction solvent.
 11. Amethod for conditioning a polymeric microfiltration membrane accordingto claim 10 , wherein the membrane comprises a polyacrylonitrilemembrane.
 12. A method for conditioning a polymeric microfiltrationmembrane according to claim 10 , wherein the membrane comprises apolysulfone membrane.
 13. A method for conditioning a polymericmicrofiltration membrane according to claim 10 , wherein said step oftreating the membrane with an intermediate solvent comprises soaking insaid intermediate solvent for at least about one-half hour.
 14. A methodfor conditioning a polymeric microfiltration membrane according to claim10 , wherein said step of treating the membrane with an extractionsolvent comprises soaking in said extraction solvent for at least aboutone-half hour.
 15. A method for conditioning a polymeric microfiltrationmembrane according to claim 10 , further comprising a step of treatingthe membrane with a mixture of intermediate solvent and extractionsolvent.
 16. A method for conditioning a polymeric microfiltrationmembrane according to claim 10 , wherein the intermediate solventcomprises ethanol, propanol, or mixture of ethanol and propanol.
 17. Amethod for conditioning a polymeric microfiltration membrane accordingto claim 10 , wherein the extraction solvent comprises hexane.
 18. Amembrane prepared by the method of claim 10 .
 19. A membrane forselective separation of phospholipids from vegetable oil miscella,comprising: (a) a conditioned polymeric microfiltration membrane which,when subjected to a soybean oil miscella containing 25 percent by weightcrude soybean oil and 75 percent by weight hexane and a phosphorouslevel of about 5,000 ppm at a transmembrane pressure of 150 psi, willprovide a steady state permeate at greater than about 65 l/hr m² havinga phosphorous level of less than about 50 ppm.
 20. A membrane accordingto claim 19 , wherein the membrane comprises polyacrylonitrile.
 21. Amembrane according to claim 19 , wherein the membrane comprisespolysulfone.
 22. A membrane according to claim 19 , wherein the steadystate permeate is provided at greater than about 80 l/hr m².
 23. Amembrane according to claim 19 , wherein the steady state permeate isprovided with a phosphorous level of less than about 25 ppm.
 24. Amethod for cleaning a conditioned polymeric microfiltration membrane,the method comprising steps of: (a) providing a conditionedmicrofiltration membrane which has been used for separation ofphospholipids from vegetable oil miscella; and (b) flushing the membranewith extraction solvent for a time sufficient to remove phospholipidsfrom said membrane.